In a coal-fired boiler using coal as fuel, massive lump of coals are pulverized into a pulverized coal by a vertical roller mill or a horizontal ball mill, and the pulverized coal is supplied together with the primary air to a burner which is a combustion apparatus.
The vertical roller mill has a housing, a pulverization table accommodated in the housing, a pressure roller that is pressed against the pulverization table, and a pressure cylinder that presses the pressure roller against the pulverization roller provided in the housing, and the massive lump of coals are supplied to the pulverization table and pulverized by the pressure roller.
In the vertical roller mill, when the rolling resistance of the pressure roller is high, or when there is a fluctuation in the rolling resistance, a slip occurs between the pulverization table and the pressure roller, and the pressure roller may cause the self-excited vibration due to the slip.
Conventionally, when the self-excited vibration occurs, there is no effective means for stopping the self-excited vibration and the vertical roller mill itself must be stopped. Therefore, there occurs a problem, such that an operation rate reduces due to the supply stop of the pulverized coal, or a processing cost increases to restart the operation of the vertical roller mill.
In addition, there is a roller mill disclosed in Patent Document 1, wherein a catching side of a pulverization roller is inclined toward a central shaft side of a rotary table, thereby a toe-in angle is formed, also a link support, which has disc springs laminated, is provided between a pressure frame and a roller bracket, an excessive pendulum operation of the pulverization roller is suppressed to an appropriate level by the link support so that the operation can be stabilized, and the self-excited vibration is prevented.
Further, there is a method for operating a vertical mill disclosed in Patent Document 2, wherein a speed of a rotary table in a vertical roller mill is adjusted, a speed for catching a raw material in a pulverization roller is optimized, and the abnormal vibration caused due to a stick-slip phenomenon is avoided.
In view of the above-described problems, the present invention provides a vertical roller mill having with a function for suppressing the self-excited vibration.